Whisk together flour, cornmeal, 2 tablespoons sugar, the baking powder, salt, and baking soda. In another bowl, whisk together buttermilk, milk, butter, and egg. Whisk wet ingredients into dry ingredients until just combined (mixture will be lumpy).
Preheat oven to 200 degrees. Heat a griddle or large nonstick skillet over medium heat. Toss blueberries with remaining 2 tablespoons sugar. Brush griddle with melted butter. Spoon batter onto griddle 1/3 cup at a time. Sprinkle with sugared blueberries, about 2 tablespoons per pancake. Cook until edges are set, 3 to 4 minutes. Flip, and cook until golden brown, about 2 minutes. Repeat with remaining batter and blueberries, adding more butter to griddle and keeping prepared pancakes warm on a baking sheet in the oven. Serve with orange-maple butter and maple syrup.